(a) Field of the Invention
The present invention relates to a paper hopper for feeding paper sheets to a device such as an electrophotographic device, and more particularly to a paper hopper in which a paper feed table can be lifted and lowered being kept in a horizontal condition and paper sheets stacked on the paper feed table are sequentially sent out from the top sheet for feeding.
(b) Description of the Prior Art
In recent years, there has been a growing demand for large-capacity paper hoppers for feeding paper sheets to a device such as an electrophotographic device, as the speed of the printing process in printers including electrophotographic devices has been remarkably increased. However, a paper hopper of the cassette type that is installed by inserting in such a device, is limited in capacity by the size of the device to which it is applied, and therefore, it has become very common to employ a paper hopper of the separation type that is installed together with and separately from the device.
There are disclosed prior paper hoppers of the separation type in the following publications.
(1) Japanese Patent Publication Laid-Open No. 60-40340 (1985)
An endless wire rope is provided at each of the opposite sides of the paper feed table. Each endless wire rope is extended in figure-of-eight fashion such that parts of the wire rope form vertical portions parallel to the ascending/descending plane of the paper feed table. The paper feed table is then fixedly attached to and suspended by the vertical portions of each wire rope in a horizontal condition so that the paper feed table can be lifted or lowered being kept in a horizontal condition by synchronously driving the endless wire ropes at the same speed and in the same direction. By means of a driving motor, the endless wire ropes are accordingly driven with the same torque in synchronization with each other, whereby a lift force is exerted to the paper feed table.
(2) Japanese Patent Publication Laid-Open No. 3-36124 (1991)
Each of the opposite sides of the paper feed table is provided with a front lift arm for lifting the front edge of the paper feed table and a rear lift arm for lifting the rear edge of the paper feed table. The front and rear lift arms are coupled to each other by a gear so as to freely pivot on their fulcrums. By allowing the front lift arms disposed at the opposite sides to pivot synchronously and the rear lift arms to pivot synchronously through the gear, the paper feed table can be lifted or lowered being kept in a horizontal condition. An extension coil spring is then provided for exerting an elastic tensile force to one of the front lift arms so that the arm pivots on its fulcrum to lift the paper feed table. Thus, a lift force is exerted to the paper feed table.